The present invention relates to methods for melting and refining a powdery or fine granular ore containing metal oxides by preliminarily reducing the ore and then melting and reducing the preliminarily reduced ore and apparatuses for melt-refining the ore and particularly to methods for melting and refining the ore by preliminarily reducing the ore by means of a reducing gas generated upon the melting and reducing the ore and then melting and reducing (referred to as "melt-reducing" hereinafter) the preliminarily reduced ore and apparatuses for melt-refining the ore.
There has been a long-felt need to develop novel methods for refining an iron ore or a metal oxide ore. Various methods have been tried and practically carried out. However, most of them had severe drawbacks.
Concerning the form of ores containing iron oxide or various metal oxides, there is a tendency that the lump ore is reduced and the powdery ore is increased. In particular, in order to improve the quality of low grade ores, mineral processings, such as magnetic separation, floatation and the like have been carried out and it is expected that the ratio of powdery ores is more increased in future. A major part of the presently operating refining furnaces needs lump ores or previously treated lump ores and powdery ores are formed into pellets, sintered ores, briquets, and the like. Such a formation needs superfluous materials, such as solvents, binders, etc., fuels and motive powers. When a firing furnace is used for such a formation during the hot step, NOx, SOx and dusts are generally formed and if these substances are directly discharged, a problem of environmental pollution occurs, so that installations for preventing the environmental pollution are built but this needs a large cost.
As a technique capable of directly using powdery ore, a roasting or a reducing process using a fluidized bed is partially practically used. However, when the preliminarily reduced powdery ore is used in an electric furnace, a converter and other melting furnaces, in most case, a binder is added thereto and the mixture is formed into briquets and the like. It has been proposed that the powdery ore be used in a process utilizing an arc furnace or plasma but the amount of electric power consumed in such process is very large and in countries where the electric power cost is high (as in Japan), this process would not be cost effective or competitive enough.
As a means for supplying the heat energy necessary for the reduction and heating, there is a means utilizing combustion heat wherein coke is burnt by using mainly air without using electric power or pure oxygen and a blast furnace for refining iron, nickel, copper, etc. uses this process. In particular, it has been well known that the iron making blast furnace is very high in efficiency as a refining furnace due to operative technical progress and by enlarging the size of furnace. But the iron making blast furnace is a high shaft furnace and in order to ensure the air permeability in the furnace, the above described lump ores or the lump formed ores are necessary and further the lump ores and coke are piled in layer-form in the furnace, so that coke having a high strength is needed. For the production of the coke having a high strength, a high caking coal having a high price, which presumably becomes insufficient in the future in view of the resources as the starting coal is necessary or when a low caking coal or a usual coal is used, an improving binder is necessary and the production cost is increased.
It has been proposed in Japanese patent application publication No. 2,103/59 or Japanese patent laid-open application No. 142,313/79 that the powdery preliminarily reduced ore prepared by preliminarily reducing powdery ore is melted and reduced in the powdery state and in the former process, a burning assistant for burning a fuel is a gas containing more than 85% of oxygen and in the latter process, the assistant is pure oxygen. In order to maintain the molten metal pool in the melt-reducing furnace at a high temperature, in the former process, a gas having CO.sub.2 /CO ratio of 1 which has an oxidizing function against Fe is evolved through a reaction of coal with oxygen, and in the latter process, carbon attached to the preliminarily reduced ore is burnt with pure oxygen. Furthermore, in the former process, the gas is oxidizing, so that iron oxide is apt to be formed into slag in unreduced state and discharged out of the furnace, and in the latter process, the unevenness of the temperature in the combustion furnace and the unevenness of the oxygen partial pressure are apt to be caused, so that the settlement of the operating condition in the melting furnace is difficult.